The FDA is implementing a new strategy to provide experimental gene therapies to patients with rare disorders without requiring traditional clinical trials. This framework could grant access to individualized treatments, but experts are divided on safety.
Dr. Senthil Bhoopalan, a genome-editing expert at St. Jude Children's Research Hospital, called it "an exciting step." But medical ethicist Arthur Caplan of NYU warned the FDA is now "willing to accept weaker evidence."
The new "plausible mechanism pathway" would allow therapies tested only in animals or with strong biological rationale, bypassing large human trials. It applies to treatments correcting single-letter DNA errors where large-scale trials are impractical. For example, cystic fibrosis affects 40,000 Americans but has hundreds of mutations, making a single gene therapy impossible.
The safety data can be extrapolated if the same delivery mechanism is used, Bhoopalan said.
Caplan agreed the pathway seems low-risk on the surface, but noted base editors have only been tested in trials with 15 participants or fewer. Without larger trials, rare side effects remain unknown. For instance, a hemophilia gene therapy trial with 134 participants revealed liver enzyme elevations and allergic reactions - side effects smaller studies missed.
The FDA outlined criteria in The New England Journal of Medicine: diseases must have clear genetic causes, such as monogenic disorders. Polygenic diseases like dementia are excluded. Doctors must also confirm that edited tissues show changes, which is difficult for organs like the liver.
"I think we have to start thinking about this as an inevitable next step," Bhoopalan said.